The present invention relates to a liquid detection method and apparatus therefor for detecting, without contacting liquid or a liquid droplet, whether or not liquid or a liquid droplet has passed or detecting the amount of liquid passed, an ink-jet printing apparatus which detects ink discharged by an ink-jet head without contacting the ink, and an ink detection method for said ink-jet printing apparatus.
Recently, printing apparatuses, employing an ink-jet method which performs printing by discharging ink onto a printing medium, are widely utilized owing to its ease of use.
In general, an ink-jet printing apparatus employs an ink-jet head having discharge orifices for discharging ink and discharge-energy generators for generating energy to discharge ink, and performs printing by driving the discharge-energy generators in accordance with print data and discharging ink droplets onto a printing medium. For the discharge-energy generators, a heating device for applying heat energy to ink, or a piezoelectric device which applies mechanical pressure is known. When a heating device is utilized as the discharge-energy generator, for instance, a heater for discharging is provided inside a nozzle, which is connected to a discharge orifice, so that the heat generated by the heater causes rapid bubble generation in the ink and pressure of the bubbles causes to discharge ink from the discharge orifice of the nozzle end.
The printing apparatus, employing the above-described ink-jet method, has been facing a problem of bubbles being gradually generated in ink inside the nozzle as time lapses or due to continuous printing operation because of gas dissolved in the ink, and resulting in ink discharge failure causing printing errors. Furthermore, ink inside the nozzle coagulates as time lapses, and the nozzle clogs, resulting in printing errors due to ink discharge failure in an image printing operation.
In order to solve such problems, recovery processing is performed for resolving discharge failure and recovering the discharging state by, for instance, sucking ink inside the nozzle from outside the ink-jet head at predetermined time intervals or at times when an ink discharge failure is detected. However, when recovery operation is performed, a large amount of ink is discharged without being used for printing, consequently wasting ink. Moreover, even if the recovery operation is performed, there is no guarantee that discharge failure will not occur again. Furthermore, if discharge failure is caused by a damaged discharge-energy generator, recovery operation cannot resolve the discharge failure.
A known method for solving the foregoing problems of ink discharge failure is to detect a nozzle causing ink discharge failure, i.e., a nozzle which does not discharge ink despite driving the discharge-energy generators of the nozzle, and perform recovery processing on that nozzle, so as to reduce the amount of ink consumption compared to the case of performing recovering processing on all nozzles. Another known method is to perform printing operation to compensate the area where printing was not performed due to ink discharge failure. As a method for detecting a nozzle causing ink discharge failure, an optical detection method, employing a light emission device and photoreceptor, is known. According to the optical detection method, ink is discharged across a light path, which extends from the light emission device to the photoreceptor, and when it is determined based on the output of the photoreceptor that the light path is intercepted by an ink droplet, normal ink discharge is determined. Since this optical detection method can perform detection without contacting the discharged ink droplet, cumbersome operation or a structure for removing attached ink is not necessary compared to other detection methods which require a contact with ink. In addition, since the detection precision of the detection portion does not deteriorate, this optical detection method is effective.
However, along with the recent improvement in printing density, the ink droplet discharged by each nozzle of an ink-jet printhead has become small. Therefore, in the aforementioned conventional optical detection method, the proportion of the amount of light, intercepted by a discharged ink droplet, to the total amount of light, emitted by the light emission device and reached the photoreceptor, is small. As a result, sufficient detection precision cannot be achieved.
The present invention has been proposed to solve the above-described conventional problems, and has as its object to provide a liquid detection method and apparatus therefor for detecting with high precision whether or not liquid or a liquid droplet has passed, or detecting the amount of liquid passed, without contacting the liquid or liquid droplet.
Furthermore, another object of the present invention is to provide an ink-jet printing apparatus which can accurately detect, without contacting ink, existence/absence of ink or the amount of ink in the path of ink discharged by a printhead, and an ink detection method for said ink-jet printing apparatus.
In order to achieve the above-described objects, a liquid detection apparatus according to the present invention has the following configuration.
More specifically, the liquid detection apparatus comprises: radiated wave detection means, arranged near passing liquid or a liquid droplet, for detecting a radiated wave radiated from the liquid or the liquid droplet and outputting a signal corresponding to the detected radiated wave; and detection means for detecting variation of the signal from said radiated wave detection means, wherein whether or not the liquid or the liquid droplet has passed is detected without contacting the passing liquid or the liquid droplet.
Furthermore, in order to achieve the above-described objects, a liquid detection method according to the present invention has the following configuration.
More specifically, whether or not liquid or a liquid droplet has passed is detected without contacting the passing liquid or the liquid droplet, by providing a sensor, detecting a radiated wave radiated from the liquid or the liquid droplet, near the passing liquid or the liquid droplet and detecting variation of an output value of the sensor.
Furthermore, in order to achieve the above-described objects, an ink-jet printing apparatus according to the present invention has the following configuration.
More specifically, the ink-jet printing apparatus for printing an image by discharging ink onto a printing medium with an ink-jet head, comprises: radiated wave detection means for detecting a radiated wave radiated from the ink discharged by the ink-jet head and outputting a signal corresponding to the detected radiated wave; and detection means for detecting variation of the signal from said radiated wave detection means, wherein whether or not the ink has passed is detected without contacting the ink.
Furthermore, in order to achieve the above-described objects, an ink detection method for an ink-jet printing apparatus according to the present invention has the following steps.
More specifically, the ink detection method for an ink-jet printing apparatus which prints an image by discharging ink onto a printing medium with an ink-jet head, comprises: a radiated wave detection step of detecting a radiated wave radiated from the ink discharged by the ink-jet head and outputting a value corresponding to the detected wave; and a detection step of detecting variation of the value detected in said radiated wave detection step, wherein whether or not the ink has passed is detected without contacting the ink.
According to an aspect of the present invention, the radiated wave is an infrared ray, and the detection means includes an infrared ray sensor.
Furthermore, it is preferable to include measurement means which measures a variation amount of the signal, detected by said detection means, by integrating the values of the signals.
Furthermore, whether or not liquid or a liquid droplet has been discharged is determined by determining a matching state between a pattern, represented by the variation detected by said detection means, and a predetermined pattern with which the liquid or liquid droplet is outputted.
Furthermore, whether or not liquid or a liquid droplet has been discharged may be determined by determining a matching state between a timing, at which the liquid or the liquid droplet is outputted according to the predetermined pattern, and a timing represented by the variation detected by said detection means.
Furthermore, whether or not liquid or a liquid droplet has been discharged may be determined by determining a matching state between a cycle, at which the liquid or the liquid droplet is outputted according to the predetermined pattern, and a cycle represented by the variation detected by said detection means.
Furthermore, whether or not liquid or a liquid droplet has been discharged may be determined by determining a matching state between a number of times of outputting the liquid or the liquid droplet according to the predetermined pattern and a number of times represented by the variation detected by said detection means.
Furthermore, the liquid or the liquid droplet is outputted according to a cycle which corresponds to a time constant of output variation detected by said detection means, and said measurement means measures the variation amount, caused by the liquid or the liquid droplet outputted, by integrating the values of said radiated wave detection means and the radiation detected by said detection means.
Furthermore, it is preferable to include heating means for heating the liquid or the liquid droplet prior to the detection of an infrared sensor, the radiated wave detection means includes the infrared sensor.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.